1. Field of the Invention
The invention relates to footwear, such as shoes or boots, such as sports footwear in particular, which include a rigid shell. The invention also relates, albeit non-exclusively, to the field of gliding sports, such as skiing, for example. The invention also relates to other types of footwear having a rigid shell, such as trail-running shoes or footwear, the upper of which includes a rigid element, such as a stiffener, a collar, or other part. The invention also relates to a pair of shoes or boots, a heating machine for shaping the shoes or boots, and a method for manufacturing footwear.
2. Description of Background and Other Information
In a known manner, a ski boot includes a rigid shell made of a plastic material, and a comfort liner made mainly of foam. Generally speaking, the shell is made of a shell base, which envelops the foot, and an upper, which extends upwardly along the user's ankle and lower leg.
The shell, because it is rigid, transmits forces between the foot and the gliding board during skiing. The liner envelops the user's foot, ensures the foot is comfortable inside the shell, and transmits to the various zones of the foot or ankle the biases/pressures to which the shell is subjected.
In order to ensure the forces are properly transmitted between the foot and the gliding apparatus, the shell and the lining should take the shape of the skier's foot to the extent possible. However, feet have complex shapes that vary from one person to another, so shells and linings are typically manufactured to fit a range of differently shaped feet.
To make it possible for the volume of the foot to adapt to a boot more closely, the shell is equipped with buckle mechanisms, or other such devices, that make it possible to modify the inner volume of the shell.
The liner must not, however, exert too much pressure locally on the foot. Too much pressure can hinder how a seasoned skier perceives biases/pressures and can give a recreational skier, i.e., a less-seasoned skier, a feeling of discomfort, which, in the long run, can tend to develop into a feeling of pain.
Conversely, the foot must not be loose in the liner caused by empty space(s) between the foot and the liner or between the shell and the liner, which results in a loss of precision in steering the ski.
Therefore, in order to adapt the boot to the volume of the foot precisely, it is known to work on the shape of the liner. The patent document FR-2788410, for example, discloses a method for the manufacture of a liner whereby pieces are cut out from the wall of the liner to diminish its thickness locally or, conversely, to add thickened portions.
It is also known to modify the volume of the liner by either injecting air or gel into pockets provided for this purpose or, conversely, by creating a depression in pockets filled with filling materials. The patent documents U.S. Pat. No. 3,758,964, U.S. Pat. No. 3,925,916, WO-01/87100, FR-2597729, EP-0672363 disclose ski boots provided with such liners. Memory shaping foams and thermoformable foams are also known to be used. Patent documents EP-0004829 and FR-2739760 describe the manufacturing and shaping of such liners made of thermoformable foam.
These techniques yield good results, but their range of application is limited because the deformation of the liner is limited by the thickness of the liner wall and the inner volume of the shell.
Therefore, in some cases, the shell itself is deformed. However, deforming a shell requires locally heating the wall at high temperature as well as the use of heavy equipment, such as a 500° C. hot-air blower, stirrup, and hydraulic piston, which are inserted in the shell to exert a pushing force against its walls, thereby resulting in a lack of precision in terms of localization and amplitude of deformation because one works on the bare shell. This work must be carried out by a specialist. A deterioration of the outer appearance of a boot in the zones which have been heated can also result.
There are also boots whose shells are made with portions having different rigidities. In particular, these boots have more flexible portions in the sensitive foot areas, especially in the areas of the malleoli and metatarsi. Patent documents EP-0916273, U.S. Pat. No. 6,474,004, and WO-2004/052134 disclose such methods of manufacture.
Further, the German utility model DE-8611889 discloses a boot including some portions made of a thermoplastic material. In order to deform the shell and adapt it to the shape of the user's foot, these portions are locally heated beyond the softening point of the thermoplastic material, which is on the order of 100° C., that is, well below the softening temperature of the remainder of the shell.
These methods of manufacture yield good results, but are not entirely satisfactory.
The object of patent documents EP-0916273 and U.S. Pat. No. 6,474,004 is to flatten the foot against reinforced areas of the shell that go around the sensitive areas of the foot. The shell is not clearly deformed and there is, therefore, no substantial improvement in comfort for a foot that would be too greatly pressured by the liner.
In the other two documents, the structure of the shell is that of a hybrid. The less rigid portions of the shell are made of a completely different material than that of the remainder of the shell. It is therefore necessary to reinforce the shell to compensate for the local loss of rigidity in these sensitive areas. The less rigid portions are weakened zones of the boot, which are less shock and wear resistant. Moreover, because the material is different, the less rigid portions have a different appearance than the remainder of the shell and they age differently.
Considering the state of the art, there is a need for an article of footwear, such as a sports boot, a ski boot in particular, which is improved in that its volume can be modified by local deformation without a significant loss of rigidity and without significantly changing the outer appearance of the boot.